Cable dispensing and retrieval

ABSTRACT

A cable dispensing and retrieval system, which may be used to dispense and retrieve communication cable for a remote controlled vehicle, dispenses a length of cable between a release point and the ground in a generally downward direction such that at least a portion of the length of cable between the release point and the ground is permitted to move along a first axis that is parallel to the ground and controls pay out and/or retrieval of the cable to maintain a point of the cable located between the release point and the ground at a predetermined point along the first axis.

TECHNICAL FIELD

This disclosure relates to automatically dispensing and/or retrievingcable from a spool.

BACKGROUND

Remote controlled vehicles, such as robots used to detect and defuselandmines, often include a communications cable that connects thevehicle to a remote control device and serves as a communications linkbetween the vehicle and a remote operator. As an operator controls thevehicle, the communications cable can become damaged if the vehicle runsover the cable or if the cable is subjected to too much tension. Risk ofcable damage is particularly acute if relatively fragile communicationscable such as fiber optic cable is used.

SUMMARY

In one aspect, the invention features a method and system forautomatically dispensing and retrieving cable from a spool that includesdispensing a length of cable between a release point and the ground in agenerally downward direction such that at least a portion of the lengthof cable between the release point and the ground is permitted to movealong a first axis that is parallel to the ground and controlling payout or retrieval of the cable to maintain the portion of the length ofcable located between the release point and the ground at apredetermined position along the first axis.

In one particular implementation a sensor (e.g., a flex sensor, opticalsensor, etc.) is used to sense the position of the cable at one or morepoints between the release point and the ground. A controller controlsthe speed and direction of a motor coupled to a spool for storing thecable to maintain the cable in its predetermined position. Thepredetermined position of the cable is a position, such as the naturalcatenary arc formed between the release point and the ground, in whichthe cable experiences no tension other than tension due to the weight ofthe cable. The system may use parallel guide bars or other mechanisms(e.g., a V-shaped bar) that define a slot that restricts the lateralmovement of a portion of the cable in directions other than along thefirst axis.

In another particular implementation, the system includes a traversemechanism for synchronizing the release point of the cable such that therelease point is in line with a point at which cable is supplied to orreleased from the spool such that the cable is stored in a level wind.The traverse mechanism may be mechanically coupled to the spool suchthat when the reel motor rotates the spool the traverse mechanismtraverses the longitudinal axis of the spool. Alternatively, thetraverse mechanism may be coupled to a traverse motor that moves thetraverse assembly along an axis parallel to a longitudinal axis of thespool. The speed and direction traverse motor may be controller tosynchronize the release point of the cable such that the release pointis in line with a point at which cable is supplied to or released fromthe spool.

In another implementation, the system includes a mechanism formaintaining a constant tension on the cable in a direction perpendicularto the longitudinal axis of the spool as cable is supplied to orreleased from the spool. The mechanism for maintaining a constanttension may include a pinch wheel and a drive wheel coupled to a motor.Cable is fed and compressed between the pinch wheel and drive wheel andthe drive wheel is coupled to a motor that operates the drive wheelmotor at a constant torque. In this implementation, the system may alsomonitor the direction of travel of both the drive wheel motor and thereel motor (e.g., using an optical encoder) to detect a fault if adirection of travel of the drive wheel motor is opposite a direction oftravel of the reel drive motor.

The system may be attached to a remote controlled vehicle and the firstaxis may be parallel with the forwards and reverse direction of travelof the vehicle.

In another aspect, the invention features a method that includesdispensing a length of cable between a release point and the ground in agenerally downward direction such that at least a portion of the lengthof cable between the release point and the ground is permitted to movealong a first axis that is parallel to the ground and is not permittedto move substantially along other axes parallel to the ground, sensing aposition (e.g., using a flex sensor) of the cable relative to a setpoint located between the release point and the ground, wherein the setpoint is located on the first axis, and controlling pay out or retrievalof the cable to maintain the cable at the set point along the firstaxis.

In one particular implementation, the method also includes dispensing alength of cable from a spool of cable and storing the cable on the spoolin a level wind. The method may also include providing a traversemechanism that moves the release point along an axis parallel to alongitudinal axis of the spool such that a line defined by the releasepoint and the point at which cable is supplied to or released from thespool is approximately perpendicular to the longitudinal axis of thespool.

In another implementation, the method further includes controlling thespeed and direction of a reel motor coupled to the spool such the cablemaintains its position at the set point along the first axis.

In another implementation, the method includes compressing cable betweena pinch wheel and a drive wheel and operating a motor coupled to thedrive wheel at a constant torque. In this implementation, the directionof the reel motor and drive wheel motor may be monitored to detect afault if a direction of travel of the drive wheel motor is opposite adirection of travel of the reel drive motor.

In another aspect, the invention features an apparatus for dispensingand retrieving a length of cable, wherein the cable is dispensed fromthe apparatus at a release point to the ground in a generally downwarddirection that includes a flexible cable guide tube located between therelease point and the ground that defines a channel having alongitudinal axis that is generally perpendicular to the ground andconfigured to receive a length of cable. The flexible cable guide tubeis further configured to permit cable located with the channel frommoving along a longitudinal axis that is generally parallel to theground. The apparatus also includes flex sensor located adjacent to theflexible cable guide tube to detect position of at least a portion ofthe cable located within the channel of the flexible cable guide tube.

In one implementation, a controller is electrically coupled to the flexsensor and is configured to receive a signal from the flex sensorindicating a detected position of the cable within the guide tube andcontrol speed and direction of cable pay out to maintain the detectedposition of the cable at a predetermined position.

In another implementation, the apparatus further includes a pair ofrails that defines a slot through which cable is passed. The slot can beconfigured to constrain lateral movement of cable in directions exceptalong the first axis. In another implementation, a scraper attached tothe flexible guide tube; the scraper has an aperture slightly largerthan an outer diameter of the cable and is configured to scrape dirt anddebris off of the cable as it is wound onto the reel.

In another implementation, the apparatus includes a rigid cable guidetube located between the release point and the ground and above theflexible guide tube. The rigid cable guide tube defines a second channelhaving a longitudinal axis that is generally perpendicular to the groundand configured to receive a length of cable. The rigid cable guide tubefurther configured to constrain cable located with the channel frommoving along a longitudinal axis that is generally parallel to theground.

In another aspect, the invention features a method that includesdispensing a length of cable stored on a spool between a release pointand the ground in a generally vertical direction, passing the length ofcable between a slot defined by two sidewalls, wherein constrainslateral motion of cable located within the slot except along alongitudinal axis, and controlling speed and direction of a reel motorcoupled to the spool to maintain a portion of the length cable locatedbetween the release point and the ground at a predetermined positionalong the longitudinal axis.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of a cable dispensing and retrieval system mountedon a remote-controlled vehicle.

FIGS. 2A-2B are side-views of a cable dispensing and retrieval system.

FIGS. 3A-3B are perspective views of a cable dispensing and retrievalsystem.

FIGS. 4A-4B are perspective views of a pinch wheel assembly for a cabledispensing and retrieval system.

FIG. 5 is a top view of a cable between two guide rails.

FIG. 6 is a control logic diagram for a cable dispensing and retrievalsystem.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Referring to FIG. 1, a remote-controlled vehicle 12 includes a cabledispensing and retrieval system 10 that automatically dispenses andretrieves communication cable 14, e.g., fiber optic cable, as thevehicle is remotely controlled by a operator 16. In some applications,the remote-controlled vehicle is used to operate in areas where radiosignals are not reliable or permissible such as parking garages,tunnels, urban setting, foreign countries and airfields or in ahazardous environment, such as an area where land mines, toxicchemicals, or radio-active materials are present.

The communications cable 14 serves as a communication link between thevehicle 12 and a remote control device 17 handled by the operator 16.Data representing vehicle control commands (e.g., forward, reverse, turnleft, turn right, etc.) is transmitted from the remote control device 17to the vehicle. Additionally, sensory data obtained from one or moresensors mounted on the vehicle is transmitted from the vehicle to adisplay and storage device such as a TV/VCR (not shown) located withinthe remote control device 17.

As the operator controls the vehicle 12, the cable dispensing andretrieval system 10 controls pay out and retrieval of cable allowing ahigh degree of freedom of movement while managing the cable to helpreduce risk of damage during operation of the vehicle. This permitsmultiple reuse of the cable and long service life.

Referring to FIG. 2A, the cable dispensing and retrieval system 10dispenses cable from a reel spool 18 and directs the cable to theground. When the vehicle is stationary and cable 14 is released at arelease point 20 and comes in contact with the ground, it naturallyforms a catenary arc A within a plane P between the release point 20 andthe ground. This natural catenary arc A of the cable is a position inwhich there is no tension on the cable between the release point and theground other than tension due to the weight of the cable between thesetwo points.

In operation, the cable dispensing and retrieval system 10 monitors theposition of a portion of the cable along its catenary arc andautomatically dispenses or retrieves cable to maintain the shape ofcatenary arc A in plane P of the cable. For example, if a user moves theremote-controlled vehicle 12 forward (indicated by the forward arrow),the catenary arc of the cable will tend to widen as more cable issuspended above the ground. However, when the cable dispensing andretrieval system 10 senses a change in the shape of the catenary arc Ain plane P, it will dispense cable at a rate of speed sufficient tomaintain the shape of the catenary arc. Similarly, if a user moves thevehicle 12 in a reverse direction (indicated by the reverse arrow), thecatenary arc of the cable will tend to narrow. When the cable dispensingand retrieval system 10 senses this change in shape of the catenary arcA in plane P, it will retrieve cable at a rate of speed sufficient tomaintain the shape of catenary arc A. By controlling dispense andretrieval of the cable to ensure that the cable maintains a particularcatenary arc shape between a release point and the ground, the systemhelps to ensure that the cable is not subject to tension or driven overwhile the user controls the vehicle.

In one implementation, a cable dispensing and retrieval system monitorschange in position of a portion of the cable between the release pointand ground along an axis parallel to the ground and controls pay out orretrieval of cable in order to maintain the monitored portion of thecable in a predetermined position. For example, as shown in FIG. 2B, amonitored portion of cable corresponds to cable located between therelease point 20 and point X. The predetermined position is preferably aposition where the cable experiences no tension other than tensioncaused by the weight of the cable, such as the position of the cablewhen the cable is in its natural catenary arc position. A cabledispensing and retrieval system controls pay out and retrieval of cableto maintain point X at its shown location along axis y. The position ofthe monitored portion of the cable can be determined using a flex sensorthat senses flexure in the cable or using a position sensor that sensesthe cable's location at point X or at other points between the releasepoint and the ground. Examples of suitable position sensors are the flexsensor, ultrasonic sensor, torque sensor, Hall effect sensor, straingage, optical infrared sensor, laser sensor, encoder, magnetoresistivesensor, capacitive bend sensor, and a potentiometer.

In addition to controlling pay out and retrieval of the cable so that itmaintains a particular catenary arc, the cable dispensing and retrievalsystem also includes a traverse assembly that ensures that the cable isdispensed and retrieved at an angle of approximately 90 degrees from thelongitudinal axis of the reel spool. The traverse assembly also ensuresthat cable is wound onto the spool in a level wind.

Referring to FIGS. 3A-3B, the cable dispensing/retrieval system 10includes a power reel assembly 24, a traverse assembly 26, and acontroller assembly 28, that are mounted to a frame 32. The cabledispensing and retrieval system 10 also includes a pinch wheel assembly22 that is mounted to the traverse assembly 26.

The power reel assembly 24 includes a reel spool 16 and axle (not shown)that is supported by a bearing tower 34 and motor tower 36. The reelspool 16 is powered by a reel drive motor 37 housed within the motortower 36. A slip joint (not shown) mounted on the reel motor receivesone end of the reel spool axle. The reel drive motor 37 drives the reelspool 16 and axle through the slip joint. A power/communications cord 40connects the reel drive motor 37 to the controller assembly 28 throughwhich electrical power and motor control signals are supplied to themotor.

The bearing tower 34 includes a bearing block assembly 38 (shown in FIG.3B) which receives the other end of the reel spool axle. One end of thecable 14 is passed through the rotary coupler 35 and is received by thecontroller (not shown) housed in the control assembly 28. The rotarycoupler 35 permits the reel to rotate in either direction withouttwisting the cable passed through the coupler.

The controller assembly 28 houses the controller (not shown) thatcontrols operation of the reel drive motor 36, pinch drive wheel motor62, and includes a system power switch 27, an emergency stop button 25,a manual feed switch 23 and a calibration button 21.

The traverse assembly 28 includes a mounting block 46 and aself-reversing screw 44 that is aligned with the longitudinal axis ofthe reel spool 16. One end of the self-reversing screw includes a pulley43 a that is mechanically coupled to a shaft 41 with a first drive belt42 and a second drive belt (not shown) located between the reel 16 andthe motor tower 36 mechanically couples the shaft 41 with the reel spool16. In particular, the second drive belt is mechanically coupled betweena pulley (not shown) on the axle of the reel 16 and a pulley (not shown)on one end of shaft 41 (i.e., the end located adjacent to the spool reel16). The first drive belt 42 is coupled between the pulley 43 a on theself-reversing screw 44 and a pulley 43 b on the shaft 41. The pulleysand drive belts are arranged such that when the reel spool 16 rotates ina first direction (e.g., clockwise) the drive belts causes theself-reversing screw 44 to rotate in the first direction; and when thereel spool rotates in the opposite direction (e.g., counter-clockwise)the self-reversing screw also rotates in the opposite direction. Thetraverse pulley ratios are selected to wind the cable on the spool toachieve wide spacing between adjacent windings. Changing the pulleyratios varies the spacing between adjacent windings, and wide spacingprovides for reliable tangle free dispensing. In one implementation, thepulley ratios are selected to produce a pseudo random homogeneous wrapdistribution, which means that cable is wound such that there are a highnumber of reel revolutions (e.g., 10,000) before the traverse assemblyretraces the same path across the reel and that the space between anadjacent winding is relatively wide.

As the self-reversing screw rotates, the mounting block traversesparallel with the longitudinal axis of the reel spool 16. Theself-reversing screw 44 is threaded such that the mounting block willswitch its direction of travel when it reaches an end of the screwwithout having the screw to change its direction of rotation. A pinchwheel assembly 22 is mounted to the mounting block 46 and thus traverseswith the mounting block. A horizontal guide bar 29 supports the lowerend of the pinch wheel assembly 22.

Referring to FIGS. 4A-4B, the pinch wheel assembly 22 includes aflexible cable guide tube 50, a cable cleaner (scraper) 51, a rigidsplit tube cable guide 53 and mounting block 57 a pair of flex sensors52 a, 52 b, two cable guide bars 54 a, 54 b, two vertical cable rollers56 a-56 b, three pinch wheels 58 a-58 c, a drive wheel 60 and a drivewheel motor 62, that are mounted to a frame 64.

Cable 14 is fed from the reel through the vertical cable rollers 56 a-56b, between the pinch wheels 58 a-58 c and drive wheel 60 wrapping aroundthe drive wheel approximately 90 degrees, through the rigid split tubecable guide 53, the flexible guide tube 50, and scraper 51, and finallybetween the cable guide bars 54 a-54 b. The pinch wheels 58 a-58 c anddrive wheel 60 are spaced such that the cable 14 is firmly held betweenthe pinch wheels and the drive wheel. The drive wheel 60 is mechanicallycoupled to a pinch drive wheel motor 62 (shown in FIG. 4B) that isconfigured to maintain a constant tension on the cable in a directionperpendicular to and away from the longitudinal axis of the reel 16. Inone implementation, the system maintains constant tension on the cablebetween the reel and the pinch drive wheel by using a current regulatorto supply current to drive wheel motor such that it maintains a constanttorque. The pinch drive wheel motor includes a receptacle 70 forreceiving a cable (not shown) that supplies electrical power to thepinch drive wheel motor and provides a communications channel fortransmitting position information from an encoder (not shown) on thepinch drive wheel motor to the system controller.

Each pinch wheel 58 a-58 c includes an adjustment screw 66 a-66 c thatadjusts a compression spring (not shown) and moves the pinch wheelcloser to or further from the drive wheel 60. An operator can adjust thepinch wheels using the adjustment screws to ensure that the pinch wheelscompress the cable against the drive wheel enough for the drive wheel tomaintain a tension on the cable without the cable slipping as it isdispensed or retrieved.

The pair of guide bars 54 a-54 b are positioned in parallel and arespaced such that they permit cable to move freely along one axis betweenthe release point and the guide bars, but prevent the cable fromsubstantially moving in other directions. For example, as shown in FIG.5, a cable 14 is located between two parallel guide bars 54 a-54 b.Here, the cable 14 is able to move along the y-axis, which is defined bythe gap between the two guide bars, but is not permitted to move alongthe x-axis. A pair of stop bars 55 a, 55 b are connected across the twocable guide bars 54 a-54 b to prevent the cable 14 from moving beyondcertain points along the y-axis. Note that cable will be able to movealong the z-axis (which is the axis normal to the x and y axis) as cableis dispensed or retrieved.

Each flex sensor 52 a, 52 b is a long, flat flexible resistor thatchanges resistance when it is flexed. The flex sensors are attached tothe guide tube 50 with, for example, adhesive or clips. The flex sensorsare oriented such that their planar surface is perpendicular to the axisalong which the cable is able to move. For example, as shown in FIG. 5,the planar surface 53 of the flex sensor 52 ais located perpendicular tothe y-axis. By orienting the flex sensor in this way, the flex sensorsdetect when the cable flexes along the y-axis, thus indicating a changein the catenary arc of the cable. If the flex sensors indicate that thecable is flexing along the y-axis, the system controller will dispenseor retrieve cable to bring the guide tube back to its set pointposition.

In this implementation, two flex sensors are positioned “back-to-back”and electrically connected in a series half bridge. The sensors can beconnected “back-to back” by adhesive for example to provide greatersignal amplitude and physical durability. By connecting the flex sensorsin a series half bridge, the sensors reduce thermal effects, providegreater signal amplitude and symmetrical performance when flexed forwardor backward versus a system that uses a single flex sensor. For example,referring again to FIG. 5, if one flex sensor 52 a is flexed by acertain amount in the forwards direction (indicated by the forwardsarrow) such that side “A” is compressed and side “B” is stretched, thesensor will have a first response. However, if it is flexed in thereverse direction by the same amount (i.e., side “A” is stretched andside “B” is compressed), it will have a second, opposite and differentresponse. If two flex sensors are connected “back-to-back”, meaning thatthey are electrically wired in series and have opposite orientation(e.g., one sensor has its side “A” facing forwards while the secondsensor has its side “B” facing forwards), the pair of sensors will havethe same (or similar) response behavior to flexure in either directionwhile providing a signal change related to the direction of flexure.

In another implementation only one flex sensor is used. The systemcontroller calibration characterizes the feedback sensor output withamount of cable dispensed and retrieved beyond the desired set pointposition thereby accepting a wide range of feedback sensor behavior.With feedback sensor characterization the control system can functionwith a wide range of feedback sensors.

The cable scraper 51 is a small rigid plastic piece that fits onto thelower end of the flexible tube 50. The cable scraper 51 has an openingthrough which the cable passes. This opening is designed to be slightlylarger than the outer diameter of the cable 14 and functions to scrapedirt and debris off of the cable as it is retrieved by the system 10.

Referring to FIG. 6, the system control logic 100 includes amicrocontroller 102 for controlling the drive wheel motor 62 (located onthe pinch wheel assembly) and the reel motor 37.

The microcontroller 102 includes a mode function 104 that controls themode of operation of the cable dispensing and retrieval system 10. Inone implementation, there are five modes of operation:

1. Calibration mode. When the system is initially powered up or ifre-calibration is selected by an operator (e.g., by pressing thecalibration button 21 on the control panel 28 or selectingre-calibration from a remote control device), the mode function 104places the system 10 in a calibration mode, which causes a calibrationfunction 106 to run. During calibration mode, the mode function 104 doesnot permit command data from the operator 108 (e.g., forward, reverse,left, right, etc.) to be supplied to the vehicle 110. After thecalibration function is complete, the mode function 104 switches thesystem to the automatic mode.

2. Automatic mode. In this mode, the pay out and retrieval of cable isautomatically controlled by the microcontroller based on flexure of theflex sensors. The mode function permits command data from the operator108 to be supplied to the vehicle 110. In addition, the mode functionalso preferably monitors vehicle commands supplied by the operator whilethe system 10 is in the automatic mode to prevent commands likely todamage the communications cable from being supplied to the vehicle. Forexample, the mode function may prevent an operator from commanding thevehicle to turn at a turn radius (e.g., a turn radius of less than threefeet) that would likely cause the vehicle to run over and potentiallydamage the cable.

3. Manual mode. In this mode, pay out and retrieval of cable is manuallycontrolled by the operator through the operator's remote control device(e.g., remote control device 17 shown in FIG. 1). The mode function 104restricts the manual mode operation to a specific operational state setat the remote control device where powered motion of the vehicle doesnot occur.

4. Off mode. In this mode, operator commands 108 are supplied to thevehicle 110 but no cable is dispensed or retrieved.

5. Forward-Retrieve mode. In this mode, the microcontroller 102 controlsthe reel motor 37 such that cable is retrieved as the vehicle movesforward (in the automatic mode cable is dispensed as the vehicle ismoved forward). This mode can be used, for example, if the vehicle hastraveled a distance in a relatively straight line and makes a 180-degreeturn and begins coming back to its starting point. Rather thandispensing cable, the forward-retrieve mode allows the operator to causethe system to retrieve the dispensed cable as the vehicle returns to itsstarting point.

An operator may switch between the operating modes via the operator'sremote control device. In addition, the operator may switch to themanual feed mode via the switch 23 provided on the control panel 28(shown in FIG. 3A).

During calibration mode, the calibration function 106 determines a gain116 and an offset 114 to apply to the signal produced by the flexsensors as well as the relationship between the signal received from thesensor and the cable's displacement. To do this, in one implementation,the operator first positions the cable to a desired catenary arcposition. This becomes the set point. Then calibration begins by firstrecording the sensor output indicating the desired set point. Then themicrocontroller 102 causes the reel motor to dispense and retrieve ameasured length of cable such that the flex sensors are flexed atseveral points over their entire operating range and readings of thesignal produced by the sensors at each point is recorded. Thecalibration function 106 takes a series of readings (e.g., every 0.1seconds or every 0.1 inch of dispensed cable) of the signal receivedfrom the flex sensor and performs a 2^(nd) order least squares fit todetermine the relationship between the signal from the sensor and thecable's displacement. From these readings, the calibration function 106also determines the gain 116 and offset 114 for the flex sensors. If thecalibration data reveals that an adjustment of the gain or offset isnecessary then the calibration function first returns the cable to theset point, then makes the gain 116 or offset 114 adjustment, and thenrepeats the data collection. This process is repeated until the sensorsignal is determined to be sufficient to provide satisfactoryperformance. This least square fit is supplied to the position errorfunction 125 then on to the PID controller 126, where it is used todetermine the Pulse Width Modulated (PWM) signal that is supplied to thedead band eliminator function 128 (described below) and then the modefunction 104 and then to the motor controller 132 of the reel motor 37.Because the response of the flex sensors will vary with temperature, thecalibration function 106 records a reading of the ambient airtemperature from a temperature sensor 118. During operation of thevehicle (e.g., in automatic, manual, stop or forward-retrieve mode), themode function 104 will alert the user that the system needs to berecalibrated if the ambient air temperature changes from the temperatureat which calibration had been performed by a certain amount (e.g., 20degrees Fahrenheit). In another implementation, the microcontroller 106automatically adjusts the gain 116 and offset 114 of the flex sensors tocompensate for temperature or changes the 2^(nd) order least squares fitequation by utilizing sensor characterization history information storedin the microcontroller memory. In this embodiment, the microcontrollermaintains predetermined data that estimates the effect of temperature onthe response of the flex sensors. Such data may be obtained throughsystem use or experiment. As temperature changes, the microcontrolleradjusts the gain, offset and set point according to the stored data.

The calibration function 106 also operates to discover the amount ofdrive signal necessary to provide to the reel motor before the motorstarts to move in either direction, which is referred to as “dead band”current. By compensating for this “dead band” current, the controllercan more precisely control the reel motor. In one implementation, whenthe system 10 is turned on, the microcontroller processes a calibrationroutine in which the microcontroller supplies a signal to the reel motorto cause it to begin to turn and records the threshold of motion signalsupplied to the reel motor. This is repeated for the opposite directionand recorded. The output of the PID controller 126 is offset by the deadband eliminator function 128 using the amount of the recorded “deadband” drive signal corresponding to each direction less any dead banddesired to remain thus reducing or eliminating the “dead band” behavior.Since dead band can change with conditions such as temperature thiscalibration can be repeated when conditions require (e.g., temperaturechanges by more than a predetermined amount) measuring and eliminatingany amount of the “dead band” behavior desired.

The calibration function also operates to determine if the pinch wheels58 a-58 c (shown in FIG. 4A) are pressing the cable against the drivewheel 60 with sufficient force so the cable is not slipping. To do this,the microcontroller 102 monitors the pinch drive wheel encoder 120 whenthe reel encoder 122 is stopped during the calibration function 106. Ifthe drive wheel encoder 120 indicates that the drive wheel moved afterthe reel motor has been stopped, then the calibration function 106determines that the cable is slipping in the pinch wheel assembly andnotifies the operator of this problem. After the operator tightens oneor more of the pinch wheels, the system can be calibrated.

In a preferred embodiment, the calibration function simultaneouslydetermines the gain, offset, relationship between sensor signal andcable displacement, dead band current and pinch wheel slippage.

Once the system has been calibrated, it is ready to operate in theautomatic and forward-retrieve modes. While operating in these modes,the microcontroller 102 receives signals from the flex sensors (whichare converted from analog to digital form via an A-D converter 124) thatindicated the displacement of the flex sensors. These signals are fedinto the microcontroller's position error function 125 and then to thePID 120, which computes a control signal. The control signal is adjustedby the dead band eliminator 122 and is fed to the mode function 104 thento the PWM 122 that commands the reel motor controller 124. This willcause payout or retrieval of cable to cause the flex sensors to returnto the set point position.

In this implementation, the drive wheel motor 144 is not directlycontrolled by the microcontroller 102, but rather is supplied withcurrent from a current regulator 142 such that the drive wheel motor 144maintains a constant torque that tends to pull the cable from the reel.

During operation in any of the modes in which cable is retrieved ordispensed, the microcontroller monitors the position readings of thedrive wheel encoder and the reel encoder to detect faults in operationof the system. In particular, the fault detection function 134 monitorsthe encoder readings to ensure that both encoders are always moving inthe same direction. If the fault detection function 134 detects that theencoders are traveling in opposite directions, this indicates that thecable has become stuck or snagged on the reel and rather thandispensing, for example, the reel is actually retrieving cable. If thefault detection function 134 detects that the encoders are traveling inopposite directions, the mode function 104 immediately shuts downoperation of both motors by sending a signal to a relay switch 130, 146to stop current from being supplied to the motors and produces an alarmand/or produces a stop motion command to the vehicle. Control may beresumed after switching to manual or off modes to attempt correction ofthe snag or end of reel condition. Similarly if the mode function 104receives a signal from the control panel indicating that the emergencystop button has been pressed 112, the mode function immediately cuts offcurrent to both motors and passes on the emergency stop condition to thevehicle control system.

In addition to detecting when the motors travel in opposite directions,the fault detection function 134 also monitors the ratio of drive wheelencoder revolutions to reel encoder revolutions to determine when thereel is about to run out of cable. For example, when the reel is full ofcable, the ratio of drive wheel encoder revolutions to one reel encoderrevolution is relatively high in comparison to when the reel is empty.When the ratio of the drive wheel encoder revolutions to reel encoderrevolutions reaches a predetermined value, the mode function 104 sendsan audio alert 140 to a speaker 142 to notify the operator that thevehicle is about to run out of cable.

The microcontroller 102 includes a communication protocol identifier 150that permits the microcontroller 102 to receive commands from a remotecontrol device using any of several different protocols. In operation,the protocol identifier analysis incoming command data and identifiesthe protocol by decoding the first one or several commands receivedusing different protocols. If a command is successfully decoded using adecoding method defined by one of the supported protocols, the protocolidentifier 150 assumes that the remote control device is using thatprotocol and begins decoding commands using the specified decodingtechnique. For example, military remote control systems may employ anyof three protocols, one which includes an 8-bit check sum protocol, asecond which includes a 16 bit cyclic redundancy check (CRC) protocol,or a third protocol called the Joint Architecture of Unmanned GroundSystems (JAUS). A protocol identifier can be configured to attempt allthree decode techniques on an initial command and automaticallydetermine which protocol is being used by seeing which decode techniqueresulted in a valid command. The ability of the communication protocolidentifier to accept one of a number of communication protocols allowsthe system to be operable with all versions of an evolving product lineas well as systems from varying product lines, manufacturers andmilitary.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, while the figures above illustrate a cable dispensing andretrieval system which is mounted to a moving vehicle, otherimplementations may utilize a similar cable dispensing and retrievalsystem in which a user (or a mechanical device) pulls cable from astationary system. For example, a worker laying communication cable mayhave a cable dispensing and retrieval system mounted to the back of awork vehicle. When the worker needs to pull some cable from the reel, heor she simply begins pulling one end of the cable. As the user pulls onthe cable, the system would detect a change in the position of themonitored portion of the cable and rotate the reel so that cable isdispensed from the reel without subjecting it to excessive tension.

The traverse assembly shown and described above is synchronized with thereel motor via a mechanical coupling. Other implementations may employ amore sophisticated traverse assembly in which the traverse is controlledby a separate motor. In these implementations, position of the traversemotor and position of the reel motor could be fed into a PID controllerto synchronize the traverse and the reel motors.

Other implementations may employ non-parallel guide bars. For example,one implementation employs a pair of angled guide bars that form aV-shape. The cable is fed between a slot defined by the angled guidebars and a sensor (e.g., flex sensor or position sensor) senses theposition of a portion of the cable between the release point and theground along one axis parallel to the ground.

In another implementation, the guide bar and sensor are configured torotate along the axis of the cable between the release point and theground based on command data received from the operator. For example, ifthe operator commands the vehicle to turn, the guide bars and sensorcould be configured to automatically rotate in the direction of the turnjust prior to the vehicle making the turn. By rotating the guide bar andsensor just prior to a turn, performance of the cable dispensing andretrieval system may be enhanced. In addition, the guide bars and sensormay be configured to rotate (either automatically or at the command ofan operator) 90 degrees when the system is employed on a turret of avehicle. For example, if the cable dispensing and retrieval system isemployed on the back of a turret of an excavator, the operator may drivethe excavator to a desired location and then begin sending command datainstructing the excavator to rotate its turret (e.g., to begin digging).When the microcontroller receives command data instructing the excavatorto rotate its turret, the microcontroller may automatically rotate atleast the guide bars and sensor by 90 degrees so that monitored axis(defined by the guide bars and sensor) of the cable is tangential to theradius of turret travel.

In yet other implementations, the microcontroller automatically augmentsthe control scheme. For example, if the microcontroller receives acommand signal instructing the vehicle to take a turn, themicrocontroller may change the set point of the control scheme so thatcable is picked up or paid out faster during the turn to avoid draggingthe cable across the ground. Similarly, the microcontroller may turn theintegrator of the PID controller off when the vehicle is stopped.

As mentioned above, the microcontroller uses the encoder ratios todetermine a volume of cable that is on the reel. In otherimplementations, the microcontroller may automatically adjust thecontrol scheme based on the volume of cable that it determines is on thereel. For example, when the reel is relatively full (thus requiring moretorque to rotate the spool) the microcontroller may adjust theproportional, integrator and differential gains of the PID controller.Similarly, as cable is pulled from the reel the microcontroller may beconfigured to automatically gradually adjust the proportional,integrator and differential gains of the PID controller.

In another implementation, the microcontroller automatically adjusts thecable tension. For example, if the microcontroller is operating in thecalibration mode and slip is detected, the pinch motor current could betemporarily adjusted to stop slippage and allow calibration to complete.Similarly the pinch motor current could be adjusted based on the reelmotor acceleration and direction.

As mentioned above, tension is applied to the cable between the reel andthe drive wheel pinch point. A second cable cleaner could be located inthis section of cable. In one implementation it could be comprised of awiper device that is in contact with the fiber during retrieve only andnot during dispense. In another implementation it could be part of apair vertical guide wheels (e.g., guide wheels 56 a and 56 b shown inFIG. 4A) and thus in contact during both directions of cable movement.

The calibration mode of a controller could use a characterization arraytechnique instead of a 2^(nd) order equation in another implementation.For example, the data collected during calibration could be stored in anarray. Sensor signals would be interpolated from the data set stored inthe calibration array.

Accordingly, other embodiments are within the scope of the followingclaims.

1. A method comprising: dispensing a length of cable between a releasepoint and the ground in a generally downward direction such that atleast a portion of the length of cable between the release point and theground is permitted to move along a first axis that is parallel to theground; and controlling pay out or retrieval of the cable to maintainthe portion of the length of cable located between the release point andthe ground at a predetermined position along the first axis.
 2. Themethod of claim 1 further comprising: sensing a position of the cablealong one or more points of the portion of the length of cable.
 3. Themethod of claim 2 wherein sensing a position comprises: using a flexsensor to sense the position in the portion of the length of cable. 4.The method of claim 1 wherein dispensing a length of cable comprises:dispensing a length of cable from a spool of cable.
 5. The method ofclaim 4 wherein the spool of cable stores cable in a level wind.
 6. Themethod of claim 5 further comprising: providing a traverse mechanism forstoring cable in a level wind as cable is retrieved.
 7. The method ofclaim 4 further comprising: providing a traverse mechanism synchronizingthe release point of the cable such that the release point is in linewith a point at which cable is supplied to or released from the spool.8. The method of claim 4 further comprising: providing a reel motorconfigured to variably rotate the spool in a clockwise orcounter-clockwise direction.
 9. The method of claim 8 whereincontrolling pay out or retrieval of cable comprises: controlling speedand direction of the reel motor to maintain the portion of the length ofcable located between the release point and the ground at apredetermined position along the first axis.
 10. The method of claim 7wherein the traverse assembly is mechanically coupled to the spool suchthat the traverse assembly traverses an axis parallel to a longitudinalaxis of the spool as the spool rotates.
 11. The method of claim 7wherein the traverse mechanism includes a traverse motor for moving thetraverse assembly along an axis parallel to a longitudinal axis of thespool.
 12. The method of claim 11 further comprising: controlling thetraverse motor to synchronize the release point of the cable such thatthe release point is in line with a point at which cable is supplied toor released from the spool.
 13. The method of claim 9 furthercomprising: maintaining a constant tension on the cable in a directionperpendicular to the longitudinal axis of the spool as cable is suppliedto or released from the spool.
 14. The method of claim 13 whereinmaintaining a constant tension comprises: compressing cable between apinch wheel and a drive wheel; and operating a motor coupled to thedrive wheel at a constant torque.
 15. The method of claim 14 furthercomprising: monitoring a direction of travel of the reel motor.
 16. Themethod of claim 15 further comprising: monitoring a direction of travelof the drive wheel motor.
 17. The method of claim 16 further comprising:detecting a fault if a direction of travel of the drive wheel motor isopposite a direction of travel of the reel drive motor.
 18. The methodof claim 1 further comprising: preventing the portion of the cable fromsubstantially moving along axes parallel to the ground other than thefirst axis.
 19. The method of claim 18 further comprising: providing afirst guide bar and a second guide bar positioned in parallel with oneanother, wherein a gap defined by the space between the first and secondguide bars defines the first axis.
 20. The method of claim 4 wherein thefirst axis is parallel with a direction of travel of the spool.
 21. Themethod of claim 1 wherein the predetermined position of the portion ofthe cable is a position in which the length of cable between the releasepoint and the ground experiences no tension other than tension from theweight of the cable.
 22. A system for dispensing and retrieving a lengthof cable, wherein the cable is dispensed at a release point to theground in a generally downward direction, the system comprising: a spooladapted to contain the cable; a motor operably connected to the spoolfor dispensing and retrieving cable from the spool; and a sensor adaptedto detect a position of a portion of the cable located between therelease point and the ground along a first axis that is parallel to theground; and a controller configured to receive a signal from the sensorindicating the detected position and to control operation of the motorbased to maintain the portion of the cable at a predetermined positionalong the first axis.
 23. The system of claim 22 further comprising:apparatus adapted to prevent the portion of the cable at the detectedposition from substantially moving along axes parallel to the groundother than the first axis.
 24. The system of claim 22 where in thesensor comprises a flex sensor.
 25. The system of claim 22 furthercomprising: a traverse mechanism adapted to supply cable to the spoolsuch that cable is wound onto the spool in a series of consecutivewindings that are located adjacent to one another to form consecutiverows of overlaying cable windings.
 26. The system of claim 25 whereinthe traverse mechanism is further adapted to dispense cable from thespool at an angle of approximately 90 degrees from a longitudinal axisof the spool.
 27. The system of claim 22 further comprising: a traversemechanism adapted to synchronize the release point of the cable suchthat a line defined by the release point and the point at which cable issupplied to or released from the spool is approximately perpendicular tothe longitudinal axis of the spool.
 28. The system of 27 wherein thetraverse assembly is mechanically coupled to the spool such that thetraverse assembly traverses an axis parallel to a longitudinal axis ofthe spool as the spool rotates.
 29. The system of claim 27 wherein thetraverse mechanism includes a traverse motor for moving the traverseassembly along an axis parallel to a longitudinal axis of the spool. 30.The system of claim 29 wherein the system further comprises: acontroller that controls the traverse motor to synchronize the releasepoint of the cable such that a line defined by the release point and thepoint at which cable is supplied to or released from the spool isapproximately perpendicular to the longitudinal axis of the spool. 31.The system of claim 22 further comprising: a pinch wheel assembly thatincludes a pinch wheel and a drive wheel located adjacent to the pinchwheel, wherein the pinch wheel assembly is adapted to compress cablebetween the pinch wheel and the drive wheel; and a drive wheel motorcoupled to the drive wheel.
 32. The system of claim 31 wherein the drivewheel motor is configured to apply a constant tension on the cable in adirection away from the spool.
 33. The system of claim 32 wherein thedrive wheel motor is configured to operate to provide a constant torque.34. A method comprising: dispensing a length of cable between a releasepoint and the ground in a generally downward direction such that atleast a portion of the length of cable between the release point and theground is permitted to move along a first axis that is parallel to theground and is not permitted to move substantially along other axesparallel to the ground; sensing a position of the cable relative to aset point located between the release point and the ground, wherein theset point is located on the first axis; and controlling pay out orretrieval of the cable to maintain the cable at the set point along thefirst axis.
 35. The method of claim 34 wherein sensing a positioncomprises: using a flex sensor to sense the position of the cablerelative to the set point.
 36. The method of claim 34 wherein dispensinga length of cable comprises: dispensing a length of cable from a spoolof cable.
 37. The method of claim 36 wherein the spool of cable storescable in a level wind.
 38. The method of claim 36 further comprising:providing a traverse mechanism for storing cable in a level wind ascable is retrieved.
 39. The method of claim 36 further comprising:providing a traverse mechanism that moves the release point along anaxis parallel to a longitudinal axis of the spool such that a linedefined by the release point and the point at which cable is supplied toor released from the spool is approximately perpendicular to thelongitudinal axis of the spool.
 40. The method of claim 34 furthercomprising: providing a reel motor configured to variably rotate thespool in a clockwise or counter-clockwise direction.
 41. The method ofclaim 40 wherein controlling pay out or retrieval of cable comprises:controlling operation of the reel motor to maintain the cable at the setpoint along the first axis.
 42. The method of claim 39 wherein thetraverse assembly is mechanically coupled to the spool such that thetraverse assembly traverses an axis parallel to a longitudinal axis ofthe spool as the spool rotates.
 43. The method of claim 39 wherein thetraverse mechanism includes a traverse motor for moving the traverseassembly along an axis parallel to a longitudinal axis of the spool. 44.The method of claim 11 further comprising: controlling the traversemotor to move the release point along an axis parallel to a longitudinalaxis of the spool such that a line defined by the release point and thepoint at which cable is supplied to or released from the spool isapproximately perpendicular to the longitudinal axis of the spool. 45.The method of claim 34 further comprising: maintaining a constanttension on the cable in a direction perpendicular to the longitudinalaxis of the spool as cable is supplied to or released from the spool.46. The method of claim 45 wherein maintain a constant tensioncomprises: compressing cable between a pinch wheel and a drive wheel;and operating a motor coupled to the drive wheel at a constant torque.47. The method of claim 46 further comprising: monitoring a direction oftravel of the reel motor.
 48. The method of claim 47 further comprising:monitoring a direction of travel of the drive wheel motor.
 49. Themethod of claim 48 further comprising: detecting a fault if a directionof travel of the drive wheel motor is opposite a direction of travel ofthe reel drive motor.
 50. Apparatus for dispensing and retrieving alength of cable, wherein the cable is dispensed from the apparatus at arelease point to the ground in a generally downward direction, theapparatus comprising: a flexible cable guide tube located between therelease point and the ground, the flexible cable guide tube defining achannel having a longitudinal axis that is generally perpendicular tothe ground and configured to receive a length of cable, the flexiblecable guide tube further configured to permit cable located with thechannel from moving along a longitudinal axis that is generally parallelto the ground; and a flex sensor located adjacent to the flexible cableguide tube to detect position of at least a portion of the cable locatedwithin the channel of the flexible cable guide tube.
 51. The apparatusof claim 50 further comprising: a controller electrically coupled to theflex sensor, the controller configured to receive a signal from the flexsensor indicating a detected position of the cable within the guide tubeand control speed and direction of cable pay out to maintain thedetected position of the cable at a predetermined position.
 52. Theapparatus of claim 50 further comprising: a pair of rails defining aslot configured to receive the cable, wherein the slot is configured toconstrain lateral movement of cable in directions except along the firstaxis.
 53. The apparatus of claim 50 further comprising: a scraperattached to the flexible guide tube, wherein the scraper defines anaperture slightly larger than an outer diameter of the cable.
 54. Theapparatus of claim 50 further comprising: a rigid cable guide tubelocated between the release point and the ground and above the flexibleguide tube, the rigid cable guide tube defining a second channel havinga longitudinal axis that is generally perpendicular to the ground andconfigured to receive a length of cable, the rigid cable guide tubefurther configured to constrain cable located with the channel frommoving along a longitudinal axis that is generally parallel to theground.
 55. A method comprising: dispensing a length of cable stored ona spool between a release point and the ground in a generally verticaldirection; passing the length of cable between a slot defined by twosidewalls, wherein constrains lateral motion of cable located within theslot except along a longitudinal axis; and controlling speed anddirection of a reel motor coupled to the spool to maintain a portion ofthe length cable located between the release point and the ground at apredetermined position along the longitudinal axis.
 56. The method ofclaim 55 further comprising: sensing a position of the cable relative tothe predetermined position at one or more points between the releasepoint and the ground.
 57. The method of claim 55 wherein sensing aposition comprises: using a flex sensor to sense the position of thecable.
 58. The method of claim 55 further comprising: providing atraverse mechanism for storing cable in a level wind on the spool ascable is retrieved.
 59. The method of claim 55 further comprising:providing a traverse mechanism synchronizing the release point of thecable such that the release point is in line with a point at which cableis supplied to or released from the spool.
 60. The method of claim 59wherein the traverse assembly is mechanically coupled to the spool suchthat the traverse assembly traverses an axis parallel to a longitudinalaxis of the spool as the spool rotates.
 61. The method of claim 60further comprising: maintaining a constant tension on the cable in adirection perpendicular to the longitudinal axis of the spool as cableis supplied to or released from the spool.
 62. The method of claim 61wherein maintaining a constant tension comprises: compressing cablebetween a pinch wheel and a drive wheel; and operating a motor coupledto the drive wheel at a constant torque.
 63. The method of claim 62further comprising: monitoring a direction of travel of the reel motor.64. The method of claim 63 further comprising: monitoring a direction oftravel of the drive wheel motor.
 65. The method of claim 64 furthercomprising: detecting a fault if a direction of travel of the drivewheel motor is opposite a direction of travel of the reel drive motor.66. The method of claim 55 wherein the predetermined position of theportion of the cable is a position in which the length of cable betweenthe release point and the ground experiences no tension other thantension from the weight of the cable.